The present invention relates to a fan motor for use in a dehumidifier, an insect repeller and so on, which fan motor is designed to realize low current, low noise and a long life.
Heretofore, there have been proposed electric fans for use in dehumidifiers (refer to Patent Documents 1 to 3, and 8, for example); however, no consideration has been given to driving electric motors by batteries and consequently these related arts are not intended to realize low current, low noise and a long life.
In the meantime, in order to reduce the power consumption of the fan motor lower, such a device is proposed which performs control over suppressing the power consumption by detecting the effect of the fan motor so as to control (decrease) the number of revolutions of the fan motor according to the extent of the effect or to intermittently drive the fan motor (refer to Patent Document 4, for example), and, for another example, which arranges the fan motor to have a single blade, using a piezo-electric element (refer to Patent Document 5, for example).
However, in case that the fan motor is arranged to have such a single blade, it will tend to become expensive because a booster circuit is required.
Although single-phase stepping motors for use in timepieces are well known as motors of a low power consumption type (e.g., Patent Documents 6 and 9), these motors are hardly applicable to fan motors as their torque is very small.
Moreover, a fan motor with a stepping motor as a drive source has been proposed by Patent Document 7; however, moment of inertia of an impeller is large at low-current driving and this makes the low-current driving infeasible as a failure to start the fan motor occurs in an out-of-phase condition.
Patent Documents 2 and 3 disclose arrangements of fan receiving portions mounted to motor shafts such that fans are driven by friction between the fans and the fan receiving portions and the arrangements are intended to stop the fans even during the rotation of the motors when equipment is skewed. However, the center of gravity of the fan may deviate from the motor shaft because a gap is radially formed between the motor shaft and the fan, which results in not only deteriorating the balance but also causing vibration and noise.
Patent Document 1
JP-UM-A-2-100631
Patent Document 2
JP-A-3-154613
Patent Document 3
JP-A-11-197438
Patent Document 4
JP-A-10-5622
Patent Document 5
JP-T-2000-513070
Patent Document 6
JP-B-61-11390
Patent Document 7
JP-A-10-136634
Patent Document 8
JP-A-5-153892
Patent Document 9
JP-A-8-255859
Under the circumstances above, a no-load current of several milliamperes has heretofore been obtained by using a DC motor with a brush in which the resistance value of a rotor is increased. The brush tends to wear down as the driving of the motor continues for many hours and a problem concerning the life of the motor is developed. Therefore, it is conceivable to use a brushless motor without any contact like the brush in order to increase the life of the motor, but only the Hall element of the brushless motor requires at least several milliamperes and the current consumption will amount to several tens of milliamperes if supply of power to other components such as a drive circuit in addition to the motor is needed. Thus, continuous driving for a prolonged time by means of a battery is hardly possible.
In the case that a sensorless motor which does not have a Hall element is employed, moreover, the starting characteristics have to be high as counter electromotive force of the coil is detected, which results in making it difficult to attain lower power consumption, thereby the expenses will run up. In the case that a stepping motor without requiring such a Hall element is used, low current driving becomes possible; however, attempting to driving an impeller having a large moment of inertia causes a failure to start and an out-of-phase condition to occur because starting torque is small and the low current driving is made difficult thereby.